Hybridization of rRNA to chromatin fractions obtained by ECTHAM-cellulose chromatography failed to reveal large differences in gene dosage among the chromatin fractions which differ markedly in composition, structure and in vitro function. Methodology for isolation of nuclei in non-aqueous media have been developed in order to allow determination of the ionic composition of the nucleus. This knowledge will allow further efforts at chromatin fractionation using the milieu existing in vivo, and hopefully reducing the changes of protein redistribution during preparation of chromatin and its fractionation. A reproducible assay method for measurement of the binding of triiodothyronine to chromatin has been developed and is being employed to study transcriptional regulation by this hormone.